Some large civil gas turbine engines have combustion equipment that uses a twin case architecture, with an inner case and an outer case. In such engines, fuel spray nozzles are usually attached to the inner case, with the fuel spray nozzles passing through the outer case in order to allow the fuel spray nozzles to be attached to the inner case. To allow the fuel spray nozzles to pass through the outer case, the outer case typically has a respective hole for each fuel spray nozzle. In practice, these holes should be sealed, otherwise pressurised air inside a cavity between the outer case and the inner case may leak out, potentially reducing the engine efficiency and/or damaging other engine components.